Cyclically operated fluid displacement machine

ABSTRACT

A displacement machine ( 10 ) comprises a housing ( 11 ), a reciprocating member ( 12 ) reciprocable linearly along an axis of reciprocation ( 13 ) in the housing ( 11 ) and defining with the housing ( 11 ) first ( 14 ) and second ( 15 ) variable volume chambers. A fluid inlet ( 17 ) is connected to the first variable volume chamber ( 14 ). A fluid outlet ( 78 ) is connected to the second variable volume chamber. An inlet value ( 16 ) allows flow of fluid through the fluid inlet ( 17 ) into the first variable volume chamber ( 14 ) and prevents flow of fluid from the first variable volume chamber ( 14 ) out of the fluid inlet ( 17 ).

The present invention relates to a cyclically operated fluiddisplacement machine.

The present invention can provide a cyclically operated fluiddisplacement machine either in the form of an engine or a compressor.

The present invention aims to provide a machine which is very simple andin particular which does not require a valve train system, separatealternator and starter motor or cam shaft. The machine of the presentinvention could be used as an engine in a hybrid vehicle, the engineproducing electrical power which would then be used by electrical motorsto power the vehicle.

U.S. Pat. No. 5,172,784 describes an arrangement for powering a hybridvehicle which comprises external combustion Stirling engines coupled tolinear generators and used in conjunction with a battery pack to powerelectric motors for a vehicle.

U.S. Pat. No. 4,924,956 describes a tandem double-acting free pistonengine comprising a housing including a cylinder having first and secondcombustion chambers at opposite ends thereof and a third combustionchamber between the ends. One double acting piston is displaceablebetween the first and third combustion chamber. A second double actingpiston is displaceable between the second and third combustion chambers.The two double acting pistons are linked so that they move in timedrelationship with each other. A linear alternator is combined in theengine by attaching one coil to each of the double acting pistons and bysurrounding the cylinder with other electrical coils, the fields ofwhich are intersected by the coils on the two pistons.

The present invention provides a cyclically operated fluid displacementmachine which comprises:

a housing;

a reciprocating member reciprocal linearly along an axis ofreciprocation in the housing and defining with the housing first andsecond variable volume chambers;

a fluid inlet connected to the first variable volume chamber;

a fluid outlet connected to the second variable volume chamber;

inlet valve means which allows flow of fluid through the fluid inletinto the first variable volume chamber and which prevents flow of fluidfrom the first variable volume chamber out of the fluid inlet;

transfer valve means which allows flow of fluid from the first variablevolume chamber to the second variable volume chamber and which preventsflow of fluid from the second variable volume chamber to the firstvariable volume chamber;

outlet valve means which allows flow of fluid from the second variablevolume chamber out of the fluid outlet and which prevents flow of fluidfrom the fluid outlet into the second variable volume chamber; wherein:

during movement of the reciprocating member in the housing in a firstdirection fluid is drawn into the first variable volume chamber and thefluid in the second variable volume chamber expelled from the secondvariable volume chamber via the fluid outlet; and

during movement of the reciprocating member in the housing in a seconddirection, opposite to the first direction, fluid is compressed in thefirst variable volume chamber and fluid is transferred from the firstvariable volume chamber via the transfer valve means to the secondvariable volume chamber;

characterised in that:

the reciprocating member comprises a middle section which extendsperpendicularly of the axis of reciprocation and two end sections onopposite sides of the middle section, each of the end sectionscomprising a wall extending generally parallel to the axis ofreciprocation and each of the end sections defining with the middlesection an open-ended cylinder open at one end;

the housing has a first piston portion which extends into a first of theopen-ended cylinders of the reciprocating member and which acts as apiston in the first open-ended cylinder with the first piston portionand the first open-ended cylinder together defining the first variablevolume chamber; and

the housing has a second piston portion which extends into a second ofthe open-ended cylinders of the reciprocating member which acts as apiston in the second open-ended cylinder with the second piston portionand the second open-ended cylinder together defining the second variablevolume chamber.

The construction of the machine given above provides an engine or acompressor which has a reduced weight at reduced cost and is simple. Ineffect, the machine has a single moving member. The machine would beideal, for instance, for use as an engine in a hybrid vehicle.

Preferably, the reciprocating member has a generally circular radialcross-section and the end sections each comprise an annular wall spacedfrom a central axis of the reciprocating member.

Making the reciprocating member circular in cross-section eases themanufacture of the machine as a whole.

Preferably, an electrical winding is provided in the housing surroundingthe reciprocating member, the electrical winding extending parallel toand adjacent to the end-section walls of the reciprocating member.

The present invention can provide a very compact and simple combinedmachine and electrical power generator. By locating the winding next tothe reciprocating member more power and/or greater electrical control isprovided. The construction of the engine can allow the greaterpercentage of the work of the piston in an engine to be extracted andalso the construction of machine allows electrical force to be usedefficiently to compress gas in a compressor or to compress fuel/airmixture in an engine. Electrical control can also be used to control theposition of the reciprocating member accurately.

Preferably, the electrical winding extends parallel to the axis ofreciprocation on the reciprocating member and has a length equivalent toat least the sum of the axial length of the reciprocating member and thedistance travelled by the reciprocating member in each reciprocation.This ensures good efficiency.

Preferably the end section walls of the reciprocating member areslidable in slots defined in the housing and the electrical winding inthe housing extends adjacent to, and parallel with, surfaces definingthe slots. Preferably a seal is formed between the end sections of thereciprocating member and the slots in which the end section slides.

In some embodiments resilient means acts between the housing and thereciprocating member to bias the reciprocating member to move in onedirection. Preferably the resilient means act to bias the reciprocatingmember to reduce the second variable volume chamber to a minimum volume.

The reciprocating member in the present machine is essentially a freemotion member. In the prior art, free motion pistons have tended to beused in diesel engines or in Stirling engines. In diesel enginescombustion could be ensured by the functioning of the diesel cycle.However, the engines tend to be fairly large and bulky. Stirling engineslack the benefit of internal combustion. The resilient means biassingthe reciprocal member could comprise a standard coiled spring or a gasspring. The machine could be configured to work at a frequencyequivalent to its resonant frequency, e.g. 3000 rpm. The machine couldalso be operated by pausing the reciprocating member at a convenientpoint, with the duration of the pause being variable to vary poweroutput.

Preferably, each of the inlet valve means, the outlet valve means andthe transfer valve means comprises either a one-way valve which opensand closes under the action of a pressure differential thereacross or aported valve comprising a port opening onto one of the variable volumechambers which is cyclically opened and closed by the reciprocatingmember during reciprocation.

The present invention can remove the need for a complicated valve trainsystem. The present invention when used as an engine can combine analternator and a starter motor by using electrical winding.

The present invention does away with the need for a cam shaft to controlmovement of valves. The present invention works essentially on atwo-stroke cycle when the invention is used as an engine.

Preferably the inlet valve means comprises a spring-biassed one-wayvalve.

In one embodiment the machine described before functions as an internalcombustion engine, wherein:

a charge of air is drawn into the first variable volume chamber via thefluid inlet;

the charge of air drawn into the first variable volume chamber iscompressed;

the compressed charge of air is delivered via the transfer valve meansto the second variable volume chamber;

the machine comprises fuel delivery means which delivers fuel to asecond variable volume chamber for mixing with the compressed charge ofair;

the compressed charge mixture of fuel and air is combusted and allowedto expand in the second variable volume chamber; and

the expanded combusted mixture is scavenged from the second variablevolume chamber by a subsequent charge of air delivered to the secondvariable volume chamber via the transfer valve means.

The present invention provides a very simple construction of engine,with essentially only one moving part.

Preferably the fuel used in the engine is compressed natural gas and themachine comprises storage means for storing natural gas in a pressurisedstate and fuel delivery means controls the flow of the pressurisednatural gas into the second variable volume chamber without use ofpumping means. The engine is made simple by the fact that no pump isneeded. The engine is made simple and light and can be used for instanceto provide enough power to drive a television and lights. Bottlednatural gas is widely available. The burning of natural gas solves lotsof emission problems, because natural gas burns very efficiently in airwithout leaving difficult problems of emissions. Indeed it is envisionedthat the engine of the present invention will run without any need fortreatment of the exhaust gases, for instance without the need of acatalytic converter.

Preferably the inlet valve means comprises a one-way valve, the transfervalve means comprises a port cyclically opened and closed during motionof the reciprocating member and the exhaust valve means comprises a portcyclically opened and closed during motion of the reciprocating member.More preferably, the transfer valve means comprises a first transfervalve which can be opened in the first variable volume chamber and asecond transfer port which can be opened in the second variable volumechamber and conduit means extending through the reciprocating member toconnect the first and second transfer ports.

The first transfer port is devised in an inwardly facing surface of anend section wall of an open ended cylinder of the reciprocating memberand the second transfer port is provided in an inwardly facing surfaceof an end section wall of the other open ended cylinder of thereciprocating member.

The present invention provides a simple construction wherein the flow ofgases passes actually through the reciprocating member itself ratherthan through the housing surrounding the reciprocating member. This is anovel approach to the passage of gases.

As mentioned above, it is preferable that a first piston portion of thehousing extends in a first of the open-ended cylinders and opens andcloses the first transfer port present in the first open ended cylinderduring reciprocation of the reciprocating member. It is also preferablethat a second piston portion of the housing extends in a second of theopen-ended cylinders and acts as a piston in the second open endedcylinder and opens and closes the second transfer port present in thesecond open ended cylinder during reciprocation of the reciprocatingmember. Ideally, the exhaust valve means comprises an exhaust port whichcan be opened in the second variable volume chamber and conduit meansextending through the reciprocating member to connect the exhaust portto the fluid outlet. The exhaust port provided will be advantageouslyprovided on the inwardly facing surface of the end section wall of thesecond open ended cylinder, the exhaust port being located opposite thesecond transfer port. It is preferred that the second piston portion ofthe housing controls the opening and closing of the exhaust port byopening and closing the exhaust port during reciprocation of thereciprocating member.

It will be appreciated that the engine is simple in construction,operates on a two-stroke cycle and uses scavenging to remove at leastsome of the combusted gas to exhaust. The scavenging will permit someexhaust gas recirculation, because some exhaust gases will inevitablyremain along with the fresh incoming charge, for subsequent combustion.This may improve the emissions of the engine.

Preferably during each reciprocation of the reciprocating member, thesecond piston portion of the housing sequentially:

opens the exhaust port to allow combusted gases to flow from the secondvariable volume chamber;

opens the second transfer port to allow admittance of a charge of airinto the second variable volume chamber to scavenge combusted gases outof the second variable volume chamber through the exhaust port and tosupply air for combustion;

closes the second transfer port to prevent air being expelled throughthe transfer port during compression; and

closes the exhaust port to seal the second variable volume chamber readyfor combustion.

Preferably, the second piston portion of the housing which acts as apiston in the second variable volume chamber is provided with a cut-outportion located adjacent the second transfer port when the secondtransfer port is open which defines a region where combustion iscommenced. Preferably, the fuel delivery means delivers fuel to theregion of the second variable volume chamber defined by the cut outportion in the second piston portion of the housing.

Preferably the fuel and air mixture is ignited by active radicalcombustion. Active radical combustion is a new combustion mechanismrecognised in the art in which the fuel/air mixture commences combustionspontaneously due to the presence of free radical ions in the mixturealong with an elevated pressure and an elevated temperature of themixture. The free radical ions are most advantageously introduced by theretention of exhaust gases in the mixture and the use of a two-strokecycle with scavenging actively assists this. Indeed, the scavengingarrangement preferred in the present invention is a well-proven systemwhich gives a well balanced distribution of fuel/air which is very goodfor auto ignition. The active radical combustion gives stable and cleancombustion, particularly when an engine is run at a steady speed. It isenvisaged that the very simple engine of the present invention will useactive radical combustion with a two-stroke cycle and will operate as asteady state or a reasonably steady state with perhaps a full loadcondition and a half-load condition.

The machine of the present invention can be provided with a sparkignition means which operates in the region of the second variablevolume chamber when ignition is commenced. The spark ignition means canbe used either instead of active radical combustion or in combinationwith active radical combustion. It is preferred that active radicalcombustion is used alongside spark ignition, because the spark ignitionwill ensure combustion at a particular time, whilst the active radicalcombustion will ensure combustion which provides very low levels ofNO_(x) hydrocarbons and carbon monoxide.

Preferably the housing has conduit means passing therethrough whichallow cooling air to be drawn from, and expelled to, the atmosphere forpassing over and cooling of the reciprocating member. The reciprocatingmember can itself have cooling passages passing therethrough which allowpassage of cooling air through the reciprocating member. Again, the useof air cooling provides a very simple engine, which does not, forinstance, require a water pump.

Preferably the engine comprises an electrical winding in the housingsurrounding the reciprocating member and the reciprocation of thereciprocating member is used to generate electrical power with theelectrical winding being connectable to an electrical load. Forinstance, the present invention could be used as an engine in a hybridvehicle. The reciprocating member can generate single phase alternatingcurrent. Three-phase alternating current would then be provided by useof an inverter. The present invention integrates the generator into theengine itself by providing an electrical coil in the cylinder liner. Theelectrical coil is therefore brought very close to the reciprocatingmember and this aids considerably the efficiency for generators.

The coil is adjacent to the reciprocating member and there is nocylinder liner in between which will attenuate the flux linkage. Theclearance between the coil and the reciprocating member can be reducedto perhaps {fraction (1/1000)} th of an inch, ensuring maximumefficiency of the electrical circuit.

The present invention provides a good combination of engine andgenerator because essentially the engine is turned inside out, with thewhat would normally be the cylinder block in fact providing the pistonsand what would normally be the piston providing the cylinders. Thisfacilitates a good interaction between the reciprocating member and thecoil surroundings.

It is envisaged that the present invention would fill the gap betweencurrent technology and fuel cell technology and could provide animmediate hybrid power solution for vehicles, where the delay to producehybrid vehicles has been in part due to the complexity and cost ofexisting engines and fuel cell systems. The present engine would also bevery useful as a static generator. The generator could be used as agenerator for electrical power for electrical actuators in a vehiclewhich are now more common and which are more efficient and more in placeof hydraulic actuators. The combined generator engine in a vehicle couldbe provided with a socket for outside uses so that the engine could notonly provide power for powering electric motors driving a vehicle, butalso external power, e.g. of 50 Hz, for powering electrical apparatusused outside the vehicle.

The present invention also provides a use of the machine described abovein its operation as an engine in which one machine is used in tandemwith a second machine, with the reciprocal members of the first andsecond machines lying on the same axis of reciprocation and with thereciprocal members of the first and second machines connected to movetogether and with the timing of both machines chosen so that whilstcombusted gases are expanded in one machine a charge of fuel and air isbeing compressed in the other machine. The coupling of the two pistonstogether would utilise the combustion of fuel and air mixture in oneengine with the subsequent expansion of gases as power for compressingcharge air in the other engine.

In a further aspect, the machine of the present invention could also beused as a compressor with the reciprocating member driven to reciprocateby electrical power supplied to the electrical winding of the machine,wherein during reciprocation:

the charge of gas is drawn into the first variable volume chamber viathe fluid inlet;

a charge of gas drawn into the first variable volume chamber iscompressed in the first variable volume chamber;

the compressed gas is delivered via the transfer valve means to thesecond variable volume chamber;

the compressed gas delivered to the second variable volume chamber iscompressed further in the second variable volume chamber;

the compressed gas in the second variable volume chamber is expelled viathe outlet means to the outlet.

Preferably the inlet valve means in the compressor embodiment of theinvention comprises a first one way valve which allows gas to pass fromthe fluid inlet into the first variable volume chamber and does notallow gas to pass from the first variable volume chamber out of thefluid inlet, the first one way valve allowing passage of gas from thefluid inlet to the first variable volume chamber only after a pressuredifferential of a first magnitude is established thereacross.

Preferably the transfer valve means comprises a second one way valvewhich allows gas to pass from the first variable volume chamber to thesecond variable volume chamber and which prevents gas flowing from thesecond variable volume chamber to the first variable volume chamber, thesecond one way valve allowing passage of gas from the first to thesecond variable volume chamber only when a pressure differential isestablished thereacross of a second magnitude.

Preferably the outlet valve means comprises a third one way valve whichallows gas to be expelled from the second variable volume chamber to thefluid outlet and prevents gas being drawn into the second variablevolume chamber via the fluid outlet, the third one way valve allowingexpulsion of gas from the second variable volume chamber only when apressure differential is established thereacross of a third magnitude.

It will be appreciated that the compressor provided by the invention isa two-stage compressor, with the gas being compressed to a first levelof pressure in the first variable volume chamber and the second level ofpressure in the second variable volume chamber. Preferably the first,second and third one way valves are spring-biassed valves.

The compressor of the present invention is simple and cheap inconstruction.

The first variable volume chamber preferably has a cross-section takenperpendicularly of the axis of reciprocation which has a first area andthe second variable volume chamber has a cross-section taken radially ofthe axis of reciprocation which has a second area smaller than the firstarea. Thus, for a given force on the reciprocating member the pressureapplied to gas in the first variable volume chamber is less than thepressure applied to the gas in the second variable volume chamber.

Preferably the housing has a first piston portion which extends into thefirst variable volume chamber and matches in radial cross-section thefirst variable volume chamber and the housing has a second pistonportion which extends into the second variable volume chamber andmatches in radial cross-section the second variable volume chamber.

The present invention achieves its simplicity of construction byreversing the usual arrangement of components. The cylinders areprovided by the reciprocating member and the pistons are provided by thestatic housing.

Preferably the inlet valve means is provided in the first piston portionof the housing and the outlet valve means is provided in the secondpiston portion. Preferably the transfer valve means is located in themiddle section of the reciprocating member.

It is preferred that the second variable volume chamber has a maximumvolume smaller than the maximum volume of the first variable volumechamber.

Preferably the engine has control means to control the electrical waveform used to power the electrical winding and thereby control the outputof the machine.

Further embodiments of the present invention will now be described withreference to the accompanying drawings, in which:

FIG. 1 is a schematic cross-section of an internal combustion engineaccording to the present invention;

FIG. 2 is a schematic cross-section taken through the internalcombustion engine of FIG. 1;

FIG. 3 is a schematic representation of a combined pair of the internalcombustion engines illustrated in FIGS. 1 and 2; and

FIG. 4 is a schematic cross-section taken through a compressor accordingto the present invention.

Turning now to FIG. 1, a cyclically operating fluid displacement machinecan be seen in the form of an internal combustion engine 10. Theinternal combustion engine 10 comprises a housing 11 in which therereciprocates a reciprocating member 12. The reciprocating member 12 isreciprocal linearly along an axis of reciprocation 13 in the housing 11.The reciprocating member 12 defines with the housing 11 a first variablevolume chamber 14 and a second variable volume chamber 15.

An inlet valve 16 in the form of a one-way spring biassed valve allowsair to be drawn from air inlet 17 into the first variable volume chamber14 and prevents flow of air from the first variable volume chamber 14out of the air inlet 17.

The reciprocating member 12 comprises a middle section 18 which extendsperpendicularly of the axis of reciprocation 13. The reciprocatingmember 12 also comprises two end sections 19 and 20 on opposite sides ofthe middle section 18. Each of the end sections 19 and 20 comprises awall extending generally parallel to the axis of reciprocation 13. Eachof the end sections 19 and 20 defines with the middle section 18 anopen-ended cylinder open at one end. The housing 11 has a first pistonportion 21 which extends into a first of the open-ended cylinders of thereciprocating member 12 and which acts as a piston in the open-endedcylinder formed by the end-section 19. The first piston portion 21 andthe first open-ended cylinder formed by the end section 19 togetherdefine the first variable volume chamber 14.

The housing 11 has a second piston portion 22 which extends into theopen ended cylinder defined by the end-section 20 and which acts as apiston in the open-ended cylinder defined by the end section 20. Thesecond piston portion 22 and the open ended cylinder formed by the endsection 20 together define the second variable volume chamber 15.Transfer of gas from the first variable volume chamber 14 to the secondvariable volume chamber 15 is permitted by three conduits 23, 24 and 25(see FIG. 2). Each conduit 23, 24, 25 runs from a transfer port whichcan open onto the first variable volume chamber 14 to a transfer portwhich can open onto a second variable volume chamber 15. For instance,as can be seen in FIG. 1, the conduit 23 runs from a transfer port 26which can open onto the variable volume chamber 14 to a transfer port 27which can open onto the variable volume chamber 15. The transfer ports26 and 27 are closed when they are aligned with and are coveredrespectively by the piston portions 21 and 22 of the housing 11. Thetransfer ports 26 and 27 are open when they are not aligned with and arenot covered respectively by the piston portions 21 and 22.

A conduit 30 extends through the reciprocating member 12 and connects anexhaust port 31 openable in the variable volume chamber 15 with anexhaust 32 of the engine 10. The exhaust port 31 is locateddiametrically opposite the transfer ports 27, 33 and 34, as can be seenin FIG. 2.

It can also be seen in FIG. 2 that the reciprocating member 12 has acircular radial cross-section. The end sections 19 and 20 of thereciprocating member 12 comprise each an annular wall spaced from thecentral axis of the reciprocating member 12, which is coincident withthe axis of reciprocation 13. Each of the end section annular walls 19and 20 are slidable in annular slots provided in the housing 11. Twoannular slots 35 and 36 are provided one at each end of the housing 11.An annular ring seal 37 acts between the end section 19 and the slots 35and an annular ring seal 38 acts between the slot 36 and the end section20.

An electrical winding 39 is provided in the housing 11 wound around thereciprocating member 12. The electrical winding 39 is annular in natureand extends parallel to and adjacent to the cylindrical outermostsurface of the reciprocating member 12. The annular electrical winding39 extends parallel to the axis of reciprocation 13 and has a lengthequivalent to at least the sum of the axial length of the reciprocatingmember 12 and the distance travelled by the reciprocating member 12during each reciprocation.

The engine 10 uses compressed natural gas as a fuel. The compressednatural gas is contained in a pressurised container 40 which isconnected by a pipe 41 to a gas injector 42. The gas injector 42regulates the flow of compressed natural gas into the second variablevolume chamber 15, but the engine 10 does not include any pumping meansfor the fuel, instead relying upon the pressure of the pressurised gasitself.

The second piston portion 22 of the housing 11 is provided with a cutout portion 43 which is located adjacent the transfer ports 27,33 and 34when the transfer ports 27, 33 and 34 are open, i.e. the reciprocatingmember 12 is in its position shown in FIG. 1, i.e. displaced to theleft, with the volume of the second variable volume chamber 15 at orclose to maximum volume and the volume of the first variable volumechamber 14 at or close to its minimum volume. The cut out portion 43defines a region in the second variable volume chamber 15 in whichcombustion is commenced. A spark plug 44 is provided to operate in theregion 43.

The housing 11 is provided with cooling air inlets such as 45 and 46.These cooling air inlets 45 and 46 as shown are valved inlets,permitting cooling air to be drawn into the housing 11, but not expelledfrom the housing 11. Instead, cooling air outlets 77 and 78 are providedat the other end of the housing 11. Cooling air ducts 47 and 48 extendlinearly along the length of the reciprocating member 12. As thereciprocating member 12 reciprocates, cooling air is drawn in throughthe cooling air inlets 45 and 46, passed through the cooling air ducts47 and 48 and expelled through the cooling air outlets 77 and 78. Infact, the cooling air exhausted through the outlet 78 is mixed withexhaust gases passing through the exhaust 32.

In operation of the engine shown in FIGS. 1 and 2 a charge of air isdrawn into the first variable volume chamber 14 via the fluid inlet 17and via the one way inlet valve 16. The air is drawn into the firstvariable volume chamber 14 as the first variable volume chamber 14increases in volume, i.e. when the reciprocating member 12 moves to theright of its position in FIG. 1. As the reciprocating member 12 moves toincrease the volume of the first variable volume chamber 14, a pressuredifferential is established across the one-way inlet valve 16 whichallows admission of air into the first variable volume chamber 14. Aircontinues to be drawn into the chamber 14 until the chamber 14 reachesits maximum volume. At this point the one way valve 16 closes and thereciprocating member 12 acts to reduce the volume of the chamber 14.

The transfer port 26 is open throughout all or the majority of travel ofthe reciprocating member 12. As the reciprocating member 12 acts toreduce the volume of the chamber 14, the air in the chamber 14 iscompressed and also displaced through the transfer port 26 into theconduits 23, 24 and 25. Initially as the reciprocating member 12 acts toreduce the volume of the chamber 14, the transfer ports 27, 33 and 34are not open to the chamber 15, because they are sealed by the pistonportion 22 of the housing 11. As the chamber 14 reaches its minimumvolume and the chamber 15 reaches it maximum volume, the transfer ports23, 24 and 25 become uncovered and the compressed air flows into thechamber 15 and scavenges from the chamber 15 combusted gases out throughthe exhaust port 31 to the exhaust 32. The air admitted via the transferports 27,33 and 34 also forms fresh charge air for the engine 10.

Once the chamber 15 has reached its maximum volume then the direction ofmotion of the reciprocating member 12 will change and the reciprocatingmember 12 will act to reduce the volume of the chamber 15 and increasethe volume of the chamber 14. The transfer ports 27, 33 and 34 are thencovered and closed by the peripheral surface of the piston portion 22.The exhaust port 31 is subsequently closed by the piston portion 22. Thechamber 15 is then closed and the air in the chamber 15 becomescompressed as the reciprocating member 12 moves to reduce the volume ofthe chamber 15.

Either when the exhaust port 31 is closed, or shortly before the exhaustport 31 becomes closed, pressurised gas is admitted to the chamber 15.The injector 42 controls the admission of pressurised gas.

The mixture of gas and air in the chamber 15 is compressed after theexhaust port 31 is closed by the reduction in volume of the chamber 15.At or about the point where the volume of the chamber 15 is at itsminimum, the spark plug 44 sparks and ignites the gas and air mixture.The combusted gas and air mixture then expands and forces thereciprocating member 12 to move as the volume of the chamber 15increases. Eventually, the exhaust port 31 is uncovered and theexpanding combusted gases can escape to the exhaust 32. The combustedgases are scavenged by the next charge of air admitted to the transferports 27, 33 and 34 and the whole cycle begins again.

The fuel/air mixture present in the chamber 15 before combustion willcontain some exhaust gas and this is preferred. It is preferred becausethe exhaust gas will contain radical ions and will enable combustion ofthe fuel/air mixture by active radical combustion. Active radicalcombustion is known in the art and will not be explained in detail inthe specification. In the preferred embodiment, active radicalcombustion occurs in parallel with combustion using spark ignition.

In the FIG. 1 embodiment of the invention the engine 10 comprises aspring 49 which acts between the housing 11 and the reciprocating member12 to bias a reciprocating member 12 into a position where the chamber15 has minimum volume and the chamber 14 has maximum volume. In thisarrangement, after the combusted gases in chamber 15 have expanded, thespring 49 uses stored energy to return the reciprocating member 12 to aposition in which the chamber 14 has maximum volume and the chamber 15minimum volume.

The reciprocation of the reciprocating member 12 will generateelectricity by means of the electrical winding 39. The electricalwinding 39 is connected to an electronic controller 50 which generatesan alternating current sinusoidal waveform on the line 51. The line 51is connected to an electrical load. The line 51 is also connected to anelectronic controller 52 which controls the ignition of the spark plug44 and controls injection of pressurised gas by the injector 42. Thecontroller 52 can determine the position of the reciprocating member 12relative to the housing 11 from the signal on the line 51.

Rather than using a spring such as spring 49, it is envisaged that twoengines 10 can be used in tandem as illustrated in FIG. 3. It can beseen in FIG. 3 that the second variable volume chamber 15 of one of theengines 10 has its maximum volume when the second variable volumechamber 15 of the other engine 10 has its minimum volume. The tworeciprocating members 12 are connected by a connecting rod 53. Theexpansion of the combusted gases in one of the engines 10 will causeboth of the reciprocating members 12 in both engines 10 to move. In thearrangement shown, there will always be expansion of combusted gases inone of the engines so that there will always be an expanding forceacting to move the reciprocating members 12. The expansion of combustedgases in one of the engines 10 acts to move the reciprocating members 12in one direction and the expansion of the combusted gas in the otherengine 10 acts to move the reciprocating members 12 in the oppositedirection.

It can be seen in FIG. 3 that the controller 50 is common to bothengines 10 and the line 51 is connected to an inverter 54 which producesthree-phase alternating current on the line 55.

It will be appreciated from the above that the engine of the presentinvention provides a combined engine and electrical generator, suitablefor use in, for instance, a hybrid electrical vehicle. In such a case,the engine would be connected to a combination of batteries and electricmotors and would power the electric motors and/or generate electricityfor storing in the batteries. It is also possible that the output linecould be connected to a load outside of the vehicle, to power otherelectrical devices.

The engine 10 of the present invention can be designed to work at aspecific frequency, which will be the natural frequency of the engine.The engine is designed to work in a steady state condition or perhaps intwo different steady state conditions. The interaction of thereciprocating member 12 and the surrounding electrical winding 39 canallow some control of reciprocation of the reciprocating member 12 byuse of the electrical controller 50. The frequency of reciprocation ofthe reciprocating member 12 and/or the amplitude of reciprocal movementcan be varied to vary the current output. The current will beproportional to a maximum velocity of the reciprocating member 12.

It is envisaged that the induction coil 39 will comprise enamelled wire.

The engine 10 described above can be started using the coil 39 poweredby an electrical source such as a battery. The controller 50 can be usedto energise the coil 39 in order to start the reciprocation of thereciprocating member 12. Once the reciprocating member 12 has startedreciprocation then the controller 52 will start injection of pressurisedgas and ignition of the spark plug 44. Timed opposing forces will beapplied on the reciprocating member 12 under the control of thecontroller 50 during starting. The two coils of the two engines 10 ofthe FIG. 3 arrangement will be controlled in tandem during starting inthe FIG. 3 arrangement. In other words, the coil 39 is used as part ofan electrical motor to start the motion of the reciprocating member aswell as a generator in extracting power from the engine. Typically thereciprocating member will be reciprocated three or four times beforecombustion is initiated.

It is envisaged that the coil 39 can be used in place of or in parallelwith a spring such as 49 to apply an electromagnetic force which acts toreduce the volume of the chamber 15 and compress the charge therein.Electrical power would be supplied to the coil 39 to enable this tohappen. As long as on average the power needed by the coil 39 to effectcompression of the fuel/air charge is less than the power extracted bythe coil from motion of the reciprocating member caused by expansion ofcombusted gases, the engine will produce electrical power. The coil canin effect act as an electrical equivalent to a flywheel. Use of a coilas the sole means of effecting compression of a fuel/air charge (withouthelp of a spring) can be beneficial in ensuring accurate control ofposition of reciprocating member 12.

The engine 10 can be operated in such a way that during operation thereciprocating member 12 can be held stationary for a pause of acontrollable duration, under the control of an electromagnetic forceapplied by coil 39. For instance, the reciprocating member 12 could beheld in a position in which the exhaust port 31 has just been closed.The coil 39 could then, after a pause, apply an electromagnetic force tocompress the fuel/air charge in the chamber 15 and operation could startagain. The use of periodically occurring variable length pauses could beused to vary the power output of the engine in place of a change of rateof reciprocation of the reciprocating member 12 since it is preferredthat the reciprocating member 12 when reciprocating does so at aconstant optimum rate.

It will be appreciated that the engine above provides a very simpleconstruction engine of light weight and low cost. The engine effectivelyhas a single moving part, the reciprocating member 12. The engine doesnot need complicated valving arrangements or cam shafts to drive suchvalves.

The cyclically operated fluid displacement machine of the presentinvention can also provide a compressor and an example of this is shownin FIG. 4. In FIG. 4 a compressor 100 is shown to comprise a housing 101in which reciprocates a reciprocating member 102. The reciprocatingmember 102 is reciprocal along an axis of reciprocation 103. Thereciprocating member 102 defines with the housing 101 a first variablevolume chamber 104 and a second variable volume chamber 105. The firstvariable volume chamber 104 has a cross-section taken radially of theaxis of reciprocation 13 which has a first area and the second variablevolume chamber 105 has a cross-section taken radially of the axis ofreciprocation 103 which has a second area smaller than the first area.The second variable volume chamber 105 has a maximum volume smaller thanthe maximum volume of the first variable volume chamber 104. A one-wayinlet valve 106 allows flow of gas from a gas inlet 107 into the firstvariable volume chamber 104, but does not allow gas to pass from thevariable volume chamber 104 out of the gas inlet 107. The one way inletvalve 106 is spring-biassed and only allows gas to flow from the gasinlet 107 into the first variable volume chamber 104 when a pressuredifferential of a first magnitude is established thereacross. Thereciprocating member 102 comprises a middle section 108 which extendsperpendicularly of the axis of reciprocation 103. The reciprocatingmember 102 has two end sections 109 and 110 on opposite sides of themiddle section 108. The end sections 109, 110 comprise walls extendinggenerally parallel to the axis of reciprocation 103. Each end section109, 110 defines with the middle section 108 an open ended cylinder,open at one end. The housing 101 has a first piston portion 111 whichextends into the open ended cylinder defined in part by the end section109. The piston portion 111 acts as a piston in the open ended cylinderdefined in part by the end section 109. The first piston portion 111 andthe open ended cylinder defined in part by the end section 109 togetherdefine the first variable volume chamber 104.

A second piston portion 112 extends into the open ended cylinder definedin part by the wall 110. The piston portion 112 acts as a piston in theopen ended cylinder defined in part by the end section 110 and the openended cylinder and the piston portion 112 together define a secondvariable volume chamber 105.

The reciprocating member 102 has a generally circular radialcross-section and the end sections 109 and 110 each comprise an annularwall spaced from the central axis of the reciprocating member 102 whichis coincident with the axis of reciprocation 103. The end section walls109 and 110 are slidable in two annular slots 113 and 114 provided atopposite ends of the housing 101. A transfer one-way valve 115 which isspring biassed is provided in the middle section 108 of thereciprocating member 102. The valve 115 allows gas to pass from thechamber 104 to the chamber 105 but does not allow gas to pass from thechamber 105 back to the chamber 104. The valve 115 is spring-biassed andonly allows gas to pass from the chamber 104 to the chamber 105 when apressure differential is established thereacross which is of a secondmagnitude.

A third one-way valve 116 which is also spring-biassed is provided inthe piston portion 112 and allows gas to be expelled from the chamber105 to a gas outlet 117. The one-way valve 116 allows gas to be expelledfrom the chamber 105 to the outlet 117 but does not allow gas to bedrawn into the chamber 105 from the outlet 117. The valve 116 isspring-biassed to allow gas to be expelled from the chamber 105 to theoutlet 117 only when a pressure differential is established thereacrossof a third magnitude.

An annular electrical winding 118 surrounds the reciprocating member 112and extends parallel to and is adjacent to the outwardly facingcylindrical surface of the reciprocating member 102. The electricalwinding 118 extends parallel to the axis of reciprocation 103 and has alength equivalent to at least the sum of the axial length of thereciprocating member 102 and the distance travelled by the reciprocatingmember 102 in each reciprocation.

The electrical winding 118 is connected to a controller 119 which isconnected to the source of electrical power 120. The controller 119supplies to the coil 118 an electrical waveform controlled in such a waythat the reciprocating member 102 is forced first one way and then theopposite way, in a timed fashion. The reciprocating member 102 ispreferably caused to reciprocate back and forth at a frequency set bythe electrical waveform supplied by the controller 119.

Starting with the volume of the chamber 104 at its minimum, thereciprocating member will be forced by the electromagnetic force appliedby the coil 118 to increase the volume of the chamber 104. Thisincreasing in volume will establish a pressure differential across theinlet valve 106 and when this pressure differential is greater than thefirst magnitude mentioned above, the inlet valve 106 will open to allowgas to be drawn in from the gas inlet 107 into the chamber 104. Once thechamber 104 reaches its maximum volume then the one way valve 106 willclose and the reciprocating member 102 will be forced by the magneticforce to reduce in volume the chamber 104. The gas in the chamber 104will therefore be compressed. When the pressure of the compressed gas inthe chamber 104 exceeds a second magnitude (mentioned above) the one wayvalve 115 will open and will allow gas to flow from the chamber 104 intothe chamber 105 (which increases in size as the chamber 104 decreases insize). When the chamber 105 reaches its maximum volume and the chamber104 reaches its minimum volume, then the one way valve 115 will closeand the reciprocating member 102 will be forced again to increase thevolume of the chamber 104 (drawing in gas as previously described)whilst at the same time reducing in volume the chamber 105. Since thechamber 105 is a of a reduced cross-sectional area, the force on thereciprocating member 102 will result in a greater pressure being appliedto the gas compressed in chamber 105. The gas compressed in chamber 105is compressed until the pressure differential across the valve 116reaches the third magnitude, at which point the valve 116 opens andallows the gas compressed in chamber 105 to escape via the gas outlet117.

It will be appreciated that the compressor 100 provided by the inventionis a two stage compressor of very simple construction. The output of thecompressor can be controlled simply by controlling the electrical waveform used to power the electrical winding 118.

The construction of the compressor 100 is unusual in that the pistonsare part of the static housing whilst the cylinders are part of areciprocating member. This construction makes good use of the fluxlinkage between the annular electrical winding 118 and the reciprocatingmember 102, which is located adjacent to the electrical winding 118. Thetwo stage compressor is effectively a single moving part machine.

Whilst above the open ended cylinders defined by the reciprocatingmember are circular in cross-section, it should be appreciated that theopen ended cylinders could be of any cross-section and the use of theterm “cylinder” should not require a circular cross-section but couldinclude, for instance, a square cross-section, an oval cross-section, arectangular cross-section or whatever shaped cross-section is mostconvenient.

Whilst in the engine 10 mentioned above the transfer ports, e.g. 26 areclosed by the piston 21 when the chamber 14 is at minimum volume, thetransfer ports opening onto the chamber 14 could be permanently open tothe chamber 14 since control of transfer between chambers 14 and 15 isgoverned by the transfer ports 27, 33 and 34 which open onto the chamber15.

In the compressor 100 or the engine 10 mentioned above the reciprocatingmember 12, 102 could be of steel with good magnetic properties.Alternatively, a coil could be provided within the reciprocating member12, 102 for instance to allow the use of a lighter member. A currentcould be run through (or induced in) such a coil to improve theperformance of the machine.

What is claimed is:
 1. A cyclically operating fluid displacement machinewhich comprises: a housing; a reciprocating member reciprocable linearlyalong an axis of reciprocation in the housing and defining with thehousing first and second variable volume chambers; a fluid inletconnected to the first variable volume chamber; a fluid outlet connectedto the second variable volume chamber; inlet valve means which allowsflow of fluid through the fluid inlet into the first variable volumechamber and which prevents flow of fluid from the first variable volumechamber out of the fluid inlet; transfer valve means which allows flowof fluid from the first variable volume chamber to the second variablevolume chamber and which prevents flow of fluid from the second variablevolume chamber to the first variable volume chamber; and outlet valvemeans which allows flow of fluid from the second variable volume chamberout of the fluid outlet and which prevents flow of fluid from the fluidoutlet into the second variable volume chamber; wherein: during movementof the reciprocating member in the housing in a first direction fluid isdrawn into the first variable volume chamber and fluid in the secondvariable volume chamber is expelled from the second variable volumechamber via the fluid outlet; during movement of the reciprocatingmember in the housing in a second direction opposite to the firstdirection fluid is compressed in the first variable volume chamber andfluid is transferred from the first variable volume chamber via thetransfer valve means to the second variable volume chamber; thereciprocating member comprises a middle section which extendsperpendicularly of the axis of reciprocation and two end sections onopposite sides of the middle section each of the end sections comprisinga wall extending generally parallel to the axis of reciprocation andeach of the end sections defining with the middle section an open-endedcylinder open at one end; the housing has a first piston portion whichextends into a first of the open-ended cylinders of the reciprocatingmember and which acts as a piston in the first open-ended cylinder withthe first piston portion and the first open-ended cylinder togetherdefining the first variable volume chamber; and the housing has a secondpiston portion which extends into a second of the open-ended cylindersof the reciprocating member and which acts as a piston in the secondopen-ended cylinder with the second piston portion and the secondopen-ended cylinder together defining the second variable volumechamber; characterized in that: the machine further comprises anelectrical winding provided in the housing surrounding the reciprocatingmember, the electrical winding extending parallel to and adjacent to theend section walls of the reciprocating member.
 2. A machine as claimedin claim 1 wherein the reciprocating member has a generally circularradial cross-section and the end sections each comprise an annular wallspaced from a central axis of the reciprocating member.
 3. A machine asclaimed in claim 1 wherein the electrical winding extends parallel tothe axis of the reciprocation of the reciprocating member and has alength equivalent at least to the sum of the axial length of thereciprocating member and the distance travelled by the reciprocatingmember in each reciprocation.
 4. A machine as claimed in claim 3 inwhich the end section walls of the reciprocating member are slidable inslots defined in the housing and the electrical winding in the housingextends adjacent to and parallel with surfaces defining the slots.
 5. Amachine as claimed in claim 4 in which a seal is formed between the endsections of the reciprocating member and the slots in which the endsection slides.
 6. A machine as claimed in claim 5 wherein resilientmeans acts between the housing and the reciprocating member to bias thereciprocating member to move in one direction.
 7. A machine as claimedin claim 6 wherein the resilient means acts to bias the reciprocatingmember to reduce the second variable volume chamber to a minimum value.8. A machine as claimed in claim 1 wherein each of the inlet valvemeans, the outlet valve means and the transfer valve means compriseseither a one-way valve which opens and closes under the action of apressure differential thereacross or a ported valve comprising a portopening onto one of the variable volume chambers which is cyclicallyopened and closed by the reciprocating member during reciprocation.
 9. Amachine as claimed in claim 8 in which the inlet valve means comprises aspring-biased one way valve.
 10. A machine as claimed in claim 1 whichfunctions as an internal combustion engine wherein: a charge of air isdrawn into the first variable volume chamber via the fluid inlet; thecharge of air drawn into the first variable volume chamber iscompressed; the compressed charge of air is delivered via the transfervalve means to the second variable volume chamber; the machine comprisesfuel delivery means which delivers fuel to the second variable volumechamber for mixing with the compressed charge of air; the compressedcharge mixture of fuel and air is combusted and allowed to expand in thesecond variable volume chamber; and the expanded combusted mixture isscavenged from the second variable volume chamber by a subsequent chargeof air delivered to the second variable volume chamber via the transfervalve means.
 11. A machine as claimed in claim 10 wherein the fuel usedis compressed natural gas and the machine comprises storage means forstoring the natural gas in a pressurised state and wherein the fueldelivery means controls flow of the pressurised natural gas into thesecond variable volume chamber without use of pumping means.
 12. Amachine as claimed in claim 10 wherein the inlet valve means comprises aone-way valve, the transfer valve means comprises a port cyclicallyopened and closed during motion of the reciprocating member and theexhaust valve means comprises a port cyclically opened and closed duringmotion of the reciprocating member.
 13. A machine as claimed in claim 12wherein the transfer valve means comprise a first transfer port whichcan be opened in the first variable volume chamber and a second transferport which can be opened in the second variable volume chamber andconduit means extending through the reciprocating member to connect thefirst and second transfer ports.
 14. A machine as claimed in claim 13wherein the first transfer port is provided in an inwardly facingsurface of an end section wall of one open-ended cylinder of thereciprocating member and the second transfer port is provided in aninwardly facing surface of an end section wall of the other open-endedcylinder of the reciprocating member.
 15. A machine as claimed in claim14 wherein the first piston portion of the housing opens and closes thefirst transfer port present in the first open-ended cylinder duringreciprocation of the reciprocating member and wherein the second pistonportion of the housing and opens and closes the second transfer portpresent in the second open-ended cylinder during reciprocation of thereciprocating member.
 16. A machine as claimed in claim 12 wherein theexhaust valve means comprise an exhaust port which can be opened in thesecond variable volume chamber and conduit means extending through thereciprocating member to connect the exhaust port to the fluid outlet.17. A machine as claimed in claim 16 wherein the exhaust port providedon the inwardly facing surface of the end section wall of the secondopen-ended cylinder, the exhaust port being located opposite the secondtransfer port.
 18. A machine as claimed in claim 17 wherein the secondpiston portion of the housing opens and closes the exhaust port duringreciprocation of the reciprocating member.
 19. A machine as claimed inclaim 18 wherein during each reciprocation of the reciprocating memberthe second piston portion of the housing sequentially: opens the exhaustport to allow combusted gases to flow from the second variable volumechamber; opens the second transfer port to allow admittance of a chargeof air into the second variable volume chamber to scavenge combustedgases out of the second variable volume chamber through the exhaust portto supply air for combustion; closes the second transfer port to preventair being expelled through the transfer port during compression; andcloses the exhaust port to seal the second variable volume chamber readyfor combustion.
 20. A machine as claimed in claim 18 wherein the secondpiston portion of the housing is provided with a cut-out portion locatedadjacent the second transfer port when the second transfer port is openwhich defines a region wherein combustion is commenced.
 21. A machine asclaimed in claim 20 wherein the fuel delivery means delivers fuel to theregion of the second variable volume chamber defined by the cut-outportion in the second piston portion of the housing.
 22. A machine asclaimed in claim 21 wherein a spark ignition means is provided tooperate in the region of the second variable volume chamber whereincombustion is commenced to ignite the compressed fuel and air mixture.23. A machine as claimed in claim 10 wherein the housing has conduitmeans passing therethrough which allow cooling air to be drawn from andexpelled to the atmosphere for passing over and cooling of thereciprocating member.
 24. A machine as claimed in claim 23 wherein thereciprocating member has cooling passages passing therethrough whichallow passage of cooling air through the reciprocating member.
 25. Useof a first machine as claimed in claim 10 in tandem with a secondmachine as claimed in claim 10 with the reciprocable members of thefirst and second machines lying on the same axis of reciprocation andwith the reciprocable members of the first and second machines connectedto move together and with the timing of both machines chosen so thatwhilst combusted gases are expanding in one machine a charge of fuel andair is being compressed in the other machine.
 26. A machine as claimedin claim 1, which functions as a compressor with the reciprocatingmember driven to reciprocate by electrical power supplied to theelectrical winding, wherein during reciprocation: a charge of gas isdrawn into the first variable volume chamber via the fluid inlet; thecharge of gas drawn into the first variable volume chamber is compressedin the first variable volume chamber; the compressed gas is deliveredvia the transfer valve means to the second variable volume chamber; thecompressed gas delivered to the second variable volume chamber iscompressed further in the second variable volume chamber; and thecompressed gas in the second variable volume chamber is expelled via theoutlet valve means to the outlet.
 27. A machine as claimed in claim 26wherein the inlet valve means comprises a first one-way valve whichallows gas to pass from the fluid inlet into the first variable volumechamber and does not allow gas to pass from the first variable volumechamber out of the fluid inlet, the first one way valve allowing passageof gas from the fluid inlet to the first variable chamber only after apressure differential of a first magnitude is established thereacross.28. A machine as claimed in claim 27 wherein the transfer valve meanscomprises a second one way valve which allows gas to pass from the firstvariable volume chamber to the second variable volume chamber and whichprevents gas flowing from the second variable volume chamber to thefirst variable volume chamber, the second one way valve allowing passageof gas from the first to the second variable volume chamber only when apressure differential is established thereacross of a second magnitude.29. A machine as claimed in claim 28 wherein the outlet valve meanscomprise a third one way valve which allows gas to be expelled from thesecond variable volume chamber to the fluid outlet and which preventsgas being drawn into the second variable volume chamber via the fluidoutlet, the third one way valve allowing expulsion of gas from thesecond variable volume chamber only when a pressure differential isestablished thereacross of a third magnitude.
 30. A machine as claimedin claim 29 wherein each of the first, second and third one-way valvesare spring biassed valves.
 31. A machine as claimed in claim 26 whereinthe first variable volume chamber has a cross-section taken radially ofthe axis of reciprocation which has a first area and the second variablevolume chamber has a cross-section taken radially of the axis ofreciprocation which has a second area smaller than the first area.
 32. Amachine as claimed in claim 31 wherein the first piston portion matchesin radial cross-section the first variable volume chamber and the secondpiston portion matches in radial cross-section the second variablevolume chamber.
 33. A machine as claimed in claim 32 wherein the inletvalve means is provided in the first piston portion and the outlet valvemeans is provided in the second piston portion.
 34. A machine as claimedin claim 33 wherein the transfer valve means is located in the middlesection of the reciprocating member.
 35. A machine as claimed in claim31 wherein the second variable volume chamber has a maximum volumesmaller than the maximum volume of the first variable volume chamber.36. A machine as claimed in claim 26 wherein the control means isprovided to control the electrical waveform used to power the electricalwinding and thereby to control output of the machine.